This invention relates to wall anchors for securing a support fastener and particularly to a cylindrical wall anchor with an outer thread for tapping into wall material such as dry wall, sheet rock and wood comprising the surface material of a hollow "wall" or similar structure. It especially relates to the construction of such a wall anchor having a central bore to pass the material of the wall which has been dislodged by the action of the distal end of the anchor. The distal or cutting end is constructed to provide a circular cut in the wall in advance of the outer threads as the distal end of the anchor is press-turned into the wall.
Prior art anchors, best typified by the self-drilling inserts disclosed in U.S. Pat. Nos. 4,601,625; 5,039,262; and 5,160,225; provide closed end drill tips which are not desirable because of the heat of friction generated between the drill and the wall material and because the wall material is pushed and compressed during the drilling process resulting in breakage of the wall material around the bore at the rear surface of the wall and thus in a weakening of the wall's capacity to retain the anchor under stress. When used to penetrate wood panelling, the wood tends to split.
U.S. Pat. No. 5,234,299 to Gianuzzi discloses an open end drill tip with a pair of saw teeth in a saw-toothed configuration which, for the most part, eliminates generating heat by the typical drill tip. However, that anchor retains the concept of drilling by providing a tapered cylindrical surface to maintain the circularity of the drilled hole, by outward radial compression against the bank of the hole, before it is tapped by the thread on the shank portion of the anchor. Also, the saw-toothed configuration has the leading; i.e., cutting edge of each revolving tooth of the drill cutting material from the tip of each saw tooth to the pointed valley where it meets the trailing edge of the next saw tooth. This results in material build-up between the teeth and surface of the hole as it is being drilled because some of the cut material is squeezed into the pointed valley which is a circumferentially limited access area to the central bore.
In my co-pending application, Ser. No. 07/965,735, filed Oct. 23, 1992, soon to be issued as U.S. Pat. No. 5,308,203, incorporated herein by reference, there is also disclosed a threaded cylindrical anchor with a through bore and saw teeth at the distal end in the form of peaks with flat valleys therebetween to provide easier access areas for the cut wall material to pass to the open end of the anchor. The threads extend along the cylindrical body of the anchor to immediately start tapping the circular cut in the wall to eliminate drilling.
In my co-pending application, Ser. No. 08/153,374, filed Nov. 10, 1993, incorporated herein by reference, there is also disclosed through bore anchors with circular saw tips of varying configuration in which access areas are provided between the tips of the multiple teeth, the cutting edges of which are outside of the diameter of the distal end of the anchor to avoid the provision of guiding surfaces about the distal end and thus avoid drilling a hole prior to tapping. In this respect, the threads on the anchor body extend between the proximal and distal ends so that tapping can commence as the circular cut is formed and before the hole is drilled. Application Ser. No. 08/153,374 also discloses a single saw tooth at the tip of the distal end of the anchor which provides the greatest amount of access area for the wall material being dislodged to the through bore.
It is an object of this invention to provide an outwardly threaded insert which has a cylindrical body with an axial through bore, a flange at its proximal end and, in one preferred embodiment of the invention, having an improved single cutter extending from the periphery of the open distal end of the anchor for first piercing the wall prior to rotation of the anchor to cut a hole in the wall and to permit the wall material around which the tip has cut to enter the axial bore so as not to be pushed and compressed and to "explode" out of the rear surface of the wall or otherwise weaken the seat of the anchor when in place.
It is another object of this invention to provide a hollow, flanged and threaded cylindrical anchor with a single drill tip disposed at the otherwise open distal end across the axis of the anchor extending between distally extended drill mounts to provide access areas on either side and under the proximal edges of the drill tip so that the drilled material will not be pushed and compressed against the wall material as the hole is being formed. The drill tip is formed to cut, or slice, into the wall material before rotation so that the drill mounts act as collectors of the material to deposit the material into the hollow of the cylindrical anchor.
In both embodiments, it is preferred to extend the thread of the anchor to the distal end so that tapping may proceed as the hole is formed. In this respect, the single drill tip of the second embodiment acts more like a cutter, although it granulates the wall material because the tapping of the hole while it is being formed prevents drilling in the sense that a hole is drilled before it is tapped.
In the embodiments of this invention, it is contemplated to provide a certain amount of outward radial compression between the anchor and wall material as the turning anchor taps the wall material and in this respect, a flat band-shaped compressor or what may be called a wedge strip is provided between the turns of the spiral thread of the anchor. In this construction, the compression between the anchor and wall between the turns of the spiral of the thread adjacent the flanged proximal end of the anchor tightens the seat of the anchor as by wedging.
As noted in co-pending application Ser. No. 08/153,374, it has been found that a saw tipped anchor having a single saw tooth saws the hole for the anchor seat more efficiently than anchors with plural saw teeth in any configuration. It is believed that this is so because the configuration of the end of the through bore at the saw toothed end is slanted across the anchor axis so that there is more area for the cut wall material to enter.
The slanted configuration of the end of the anchor adjacent the improved single cutter of this invention is maintained in the configurations of the present invention. The configuration of the cutter, however, has been designed to provide a pointed knife tip and, in the first embodiment, a leading cutting edge more or less parallel to the anchor axis, with the periphery of the anchor end extending from the trailing edge of the cutter to the proximal end of the leading edge in a spiral path. Thus, having the access area about the periphery of the bore at the cutting end of the anchor shaped to collect the wall material as it is cut.
In the second embodiment of the invention, the drill tip is, in fact, a knife disposed across the otherwise open end of the anchor and the drill mounts diverge in a curved; i.e., spiral path proximally along the periphery of the distal end of the anchor to act as collectors of the drilled material as the anchor is rotated.
It is contemplated by this invention that the flanged end of the insert is provided with a recess for receiving a drive tool, such as a screw driver, for rotating the entry end against and through the wall board and that the interior of the axial bore of the insert is splined along its proximal extension so that a screw fastener may tap the splines as it is screwed into the insert. It is also contemplated by this invention that the distal extension which has captured the material passed the knife of the entry end, extends passed the rear surface of the wall board. Resultingly, the screw fastener, which may be longer than the width of the wall board, after tapping into the splines of the axial bore may then thread into the captured material or act to push the material out of the entry end of the anchor.
In a preferred embodiment of the invention, the outer diameter of the proximal extension of the anchor increases from its juncture with the distal extension to its flanged end, while the distal extension of the insert comprises a straight cylinder with a slightly smaller outside diameter than the increasing outside diameter of the flanged proximal extension.
The cylindrical body may be outwardly threaded substantially along its entire length with the height of the thread increasing from the entry end; i.e., distal end, to the flanged end inasmuch as the cutting action of the cutter and drill as they are inserted in the wall facilitates a quick insertion and immediate threading by the entry of the threads into the wall material. The increase in the height of the thread from distal end to proximal end together with the increase in diameter of the proximal extension results in a gradual increase in the size of the tapping in the wall material to more gently push the wall material radially about the increasing height of the thread around the insert, thus, again avoiding "exploding" the wall material about the insert during insertion while providing a strong grip between the wall material and insert when in place.
It has also been found that the disposition of the thread around the body of the insert close to the entry end results in a pulling action on the insert just as the single cutter or drill enters the wall and thus a facile installation.
The inventive anchors as disclosed are designed for insertion into wall board and more resistant materials such as wood and may be molded of strong plastic materials such as nylon or a mixture of nylon and KEVLAR (a trademark of DuPont) combined but which may also be made of less strong plastics inasmuch as the friction normally resulting because of drilling operations of prior art inserts, is diminished because of the cutting ends of the inserts of the invention. These inserts may also be cast in zinc.